The deal allows all Pay with Square users to find their closest Starbucks in the Square Directory using either their iPhone or Android device. Not only does Square get $25 million in a Series D financing ( reportedly valuing the company at $3.25 billion), but Starbucks CEO Howard Schultz is joining Square's board.

"We're proud that Starbucks chose Square, as we share the value of always putting customers first," Dorsey said in the press release. "More than 2 million individuals and businesses can already use Square. This partnership will accelerate our ability to provide them with the tools they need to grow their business and thrive in today's economy."

Companies like Google(GOOG) , eBay(EBAY) (via PayPal), Visa(V) and MasterCard(MA) have brought their offerings to the customer with varying degrees of success (PayPal being the most well-known). But this deal has a huge impact on the industry,said Brian Sozzi, chief equities analyst at NBG Productions and Real Money contributor. "I think it's Starbucks trying to localize themselves. It's a great thing to be able to pay with the thing in your pocket. This transforms the industry."

Starbucks did $3.3 billion in revenue in the third quarter , with a healthy portion of those transactions being credit and debit-card sales. Starbucks does not break down the percentage of payments.

Starbucks has been at the forefront of the mobile payment revolution with its own mobile payment app, but this puts the mobile payments industry on another level. "Starbucks has scale with ~7,000 U.S. stores (~4,000 licensed), and the partnership will likely be a key reference case for awareness of mobile retailing," JPMorgan wrote in a research note discussing the deal.

According to data from Ernst & Young , mobile payments are expected to be big business, with the market reaching a massive $245 billion by 2014. This deal with Starbucks puts Square in a position to capture a significant portion of that market, as the shift in payment methods continues to move away from credit cards, debit cards and cash to smartphones, tablets and other mobile devices.

This deal might even impact Apple(AAPL) , which announced its Passbook app at its Worldwide Developer Conference earlier this year, showcasing Starbucks as part of the presentation. An Apple spokesman could not be immediately reached for comment.